Printing timer



Dec., 9 1958 w. E. EVANS ET AL 2,863,938

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QN@ hm PRILJTING TIMER William E. Evans, Menlo Park, and Wadsworth E.Pohl and Thomas P. Dixon, Los Angeles, and Edgar Warner Hopf, deceased,late of Palo Alto, Calif., by Maria lsabel Hopf, administratrix, PaloAlto, Calif., assignors to Technicolor Motion Picture Corporation,Hollywood, Calif., a corporation of Maine Application .lune lo, 1954,Serial No. 437,258

2l. Claims. (Cl. l78-5.4)

This invention relates to apparatus for reproducing images on one mediumwhich are recorded on another. More particularly, the invention relatesto apparatus which employs electronic control and monitoring devices fordetermining printing parameters when it is desired to reproduce an imageon a recording medium and such medium differs in its characteristicsfrom the medium from which the image is obtained.

A specific adaptation of the invention is in the iield of color motionpicture photography wherein the imbibition printing method is employed.In such a method, as more fully described in United States Patent No1,707,699, issued to W. E. Whitney `on April 2, 1929, the originalphotographic record of a scene consists of three silver separationnegatives, each corresponding to one of the three primary image aspectsof a color scene. From these three negatives are printed threecorresponding matrices; these matrices, each of which carries a dye ofproper color, are employed to print, in sequence, and in properregistration, three-color, subtractive primary components -of the imageupon a tilm to form the iinal positive print.

ln such process it is essential that the three image aspects be balancedproperly. Thus, in order that a tinal print be obtained, it is necessarythat each matrix balance each of the other two matrices. Thisrequirement makes the step of printing matrices from separationnegatives diicult and time consuming. Since not only may the separationnegatives themselves be unbalanced with respect to each other, but alsothe density characteristics of the negatives and matrices may differ,the result is that, in the conventional practice of the imbibitionprocess, proper exposure for matrix printing is in large measuredetermined empirically. Thus, the operator can only examine the threenegatives and, from past experience, select what he believes to be anappropriate exposure for printing each of the three matrices. Next, theproper dyes are applied to each matrix and an actual positive print ismade. This print is then examined for color deciencies; based upon suchexamination, the exposures of the printers are corrected and the entireprocess is repeated. This trial and error method is continued until asatisfactory print is obtained. While the experience `of the operatorwill determine, in large measure, the number of corrections which mustbe made, even the most skilled of operators will normally be required tomake several corrections to the original printing times chosen. Theresult is that the determination of the proper exposure for matrixprinting is a time-consuming and expensive operation.

In accordance with the present invention, means are provided whereby avisual image in color, corresponding to the nal print, is obtainedelectronically from the photographic negatives. Various circuits havingthe proper characteristics are employed, such that the operator maybalance the three-color components at the desired density levels toobtain a visual picture on a cathode-ray monitor of the desired quality.From the position of the control elements for the various circuitsemployed,

States Patent Patented Dec. 9, 1958 the exposure for each of the threematrix printers may be obtained directly, with the result that thetrial-anderror method heretofore employed may be avoided.

The response characteristics of the various circuits in-I corporated aresuch as to compensate for the different characteristics of the variousmedia employed, in order that information as to the photographicparameters sought can be obtained directly from the electronic equipmentemployed.

Accordingly, it is the general object of the invention to provide anelectronic device for obtaining transfer parameters when it is desiredtorecord on a particular medium a record contained on a different mediumhaving different characteristics.

It is a further object 'of the present invention to provide such adevice wherein several components of a composite image must be balancedeach with respect to the other and wherein an optical presentation ofthe composite image is produced.

It is a more specic object of the invention to provide a device forcolor photography whereby the image aspects of the component colors canbe balanced and adjusted by visual inspection of an electronicallyobtained optical image.

Another object of the present invention is to provide apparatus tosimulate electronically the photographic process of printing to providethereby data on parameters involved in the performance of thephotographic process.

Still another object of the present invention is to provide anelectronic system wherein a positive picture in color is presented fromsilver separation negatives or integral tripack color negatives.

These and other objects of this invention are achieved by providing asystem wherein signals representative of the optical transmission ofdiscrete areas of a color record are generated and applied to separatechannels, each of which is associated with a different color imageaspect. In each channel the signals are converted to densityrepresentative signals. The average level of the density representativesignals is then established by a controllable peak-clipping circuit. Thepeak-clipping circuit output is applied to a linear contrast controlamplierpwhose gain is controllable. The output of the linear amplifieris applied to a photo-curve amplifier, which modifies the signalsapplied to it in accordance with a desired relationship between densityand cathoderay tube screen brightness and also to compensate fornonlinearities in the brightness transfer characteristics of acathode-ray tube employed at the output. In one embodiment the signalsfrom each of the photo-curve ampliiers are respectively applied to acathode-ray tube at the output of each channel. Each of these has ascreen phosphor which provides an additive color corresponding to thecolor represented by the color image aspect asso ciated with thechannel.

The images on the cathode-ray tube screens are superimposed to present acomposite picture in color. The contrast of each color and, thereby,that of the cornposite picture is controlled by varying the gain of thelinear amplier. The brightness of each color and, thereby, the colorbalance of the picture may be controlled by clipping the signals in eachchannel at different levels with the peak-clipping circuit. Calibratedcontrols are associated with each of these circuits, so that, aftervarying these controls to establish a picture having a desired colorbalance and contrast, the calibrations may be read to provideinformation as to the proper contrast and printer-light illuminationrequired to provide a positive photographic print having substantiallythe same contrast and color balance. In the event that there is overlapin the color characteristics of ther u dyes used to make the positiveprint, circuit means are provided between and in each channel tosimulate the same type of overlap reproduction in the electronicallypresented positive picture.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself, both as to its organization and method of operation, as well asadditional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanyingdrawings, in which:

Figure l is a schematic diagram of one embodiment of the invention;

Figures 2 through 2G are curves representative of the transfercharacteristic of the apparatus used in the embodiment of the inventionshown in Figure l;

Figures 3 through 3H are curves of the transfer characteristics of thesystem at various points in a. channel;

Figure 4 is a test negative;

Figures 4A through 4E are video waveforms taken at various points in achannel when the test negative is scanned;

Figure 4F shows the positive, corresponding to the negative shown inFigure 4, presented on a cathode-ray tube at the output of a channel;

Figure 5 is a circuit diagram of a logarithmic amplitier, peak clipper,and clamp used in the embodiment of the invention;

Figure 6 is a circuit diagram of the printer-light control used in theembodiment of the invention;

Figure 7 is a circuit diagram of a variable linear amplifier andcontrast control used in the embodiment of the invention;

Figure 8 is a circuit diagram of a corrective network;

Figure 9 shows curves of density versus wavelength for typical dyes usedin color photography; and

Figure l0 is a circuit diagram of another and preferred embodiment of acorrective network.

Reference is now made to Figure l, which shows in schematic form anembodiment of this invention. A flying-spot scanner tube 10 is used toprovide a scanning light beam. This is split into three scanning beamsby three objective lenses 12, 12', 12". The three beams are directedonto corresponding areas of three separation negatives 14, 14', 14,respectively representing red, green, and blue. These separationnegatives are made by well-known photographic techniques and need not bedescribed here. The three scanning beams of light scan the threenegatives in such manner that the discrete area covered by each beam atany one time on each negative corresponds to that on the othernegatives.

The output from each negative is collected by means of a lens 16, 16',16 and directed to fall upon a separate phototube 18, 18', 18". Eachphototube generates a signal whose amplitude is representative of thetransmission of the light beam through the negative of the discrete areaupon which the light impinges. Each phototube output is then applied toa video preamplifier 20, 20', 20" which ampliies the signal and providesa negttive-going signal at its output.

A dying-spot scanner tube, phototube pickup, and preamplifier of asuitable type are well known in the television field and may be founddescribed, for example, in Television Engineering, page 91, et seq., byFink, published by the McGraw-Hill Book Company. These are referred toas a liying spot camera. The yingspot scanner tube may have its beamdetiected in accordance with the United States commercial televisionstandards; namely, 525 lines in 60 fields or 30 frames per second,although these scanning ratios are by no means critical.

Since the iiying-spot scanner is being deflected in accordance withstandard television practice, the signal obtained at the output of theviedo preamplifier will be, for each une, a video signal accompanied bya pedestal signal. The type of signal obtained is shown in Figure 4A.The pedestal signal occurs during the retrace interval required betweenthe time the beam of the scanner tube reaches the end of one line and isturned oitv until it is positioned at the beginning of the next line. Itshould be noted here that each color image aspect has associatedtherewith a separate channel which includes the phototube pickup forthat aspect, a cathode-ray tube at the end of the channel, andintervening apparatus. Each channel contains substantially similarapparatus, and, accordingly, only one will be described. However, itshould be understood that thc description o one applies to each channelexcept where otherwise noted. A clamp 2.2, 22, 22 is used to restore thepeak level of the pedestai to a desired value, which, in this instance,is zero voltage.

The video preamplifier output, after being clamped, is tl en applied toa logarithmic amplifier 2d, 24', 24". This consists of an amplitierwhose output is proportional to the logarithm of its input over themajor portion of its range, as may be seen by a plot of its transfercharacteristic in Figure 2C.

Referring now to Figure 2, the curve snown is 4a plot of thc transfercharacteristic of a negative. It shows how much light is transmitted toa phototube through a negative of varying density. Figure 2A is a curveof the transfer characteristic of the phototubc 18, 18', 18". This showsthat the output is linearly related to the input, or the output voltageis linearly related to the phototuoe illumination. Similarly, the videopreamplitier 20, 21.0', 2G" has linear characteristics as shown by thecurve in Figure 2B, which consists of a plot of the input versus theoutput voltage. The curve in Figure 2C is the plot of the transfercharacteristics of the logarithmic amplifier 24, 24', 24 and shows thatthe output voltage is substantially proportional to the logarithm of theinput voltage.

The output of the logarithmic amplilier is applied to a pedestal ciipper26, 26', 26". This circuit enables clipping of the pedestal of a videosignal at a desired D. C. level, and the fact that the level is variablecan be seen from the rectangle shown coupled thereto which is called theprinter-light control 28, 22. 23". The printer-light control includes acalibrated indicator variable therewith. The reason for the nameprinter-light control will be explained subsequently. The transfercharacteristic is shown in the curve in Figure 2D. Three differentclipping level curves are shown, and it will be that for a given settingof the pedestal clipper no voltage outnut is provided until the levelset is exceeded. After this the output varies linearly with the inputfor the signal in excess of the clipping level. As may be observed fromthe curve, the pedestal clipper enables lateral translation of thecharacteristic curve. The pedestal clipper' output is then applied to avariable-gain linear amplifier 3U, 3d', 30". lts gain is variable andct'tntrolluble, as may be seen from the rectangle connected thereto,which is designated as a contrast control 3?., 32. 32". The contrastcontrol includes a calibrated indicator coupled to the amplifier-gaincontrol. The reason for designating it as a contrast control will besubsequently explained. The amplifier output is linearly related to itsinput, as may be seen by the transfer' characteristic curve shown inFigure 2E. The three different curves shown are for three differentsettings for the contrast control, just as the three different curvesshown in Figure are for three different settings of the printerlightcontrol. lt will be seen that the slope of the input versus output curvevaries with cach setting of the contrast control.

The output of the variable-gain linear amplifier is again clamped bymeans of a clamping circuit 34, 34. 34". The clamping level selected iszero volts. The signal from the linear amplifier is then applied to aphotoship may readily be plotted as a curve.

lvcurve amplifier 36, 36.',.36'- This consists of an'amplifier whichserves a twofold purpose.l First, a desired relationship between signalamplitude and cathode-ray tube screen brightness is determined. As willbe shown later, the signals presented to the photo-curve amplifier ineffect represent the density of the negative being scanned.Photographically speaking, for any given set of parameters, thebrightness of a positive at any particular point is determined by thedensity of the corresponding negative at the same point. This relation-Since it is desired to present a positive picture on a cathode-ray tubescreen from density representative signals, a curve, which is anelectronic analogue of the density versus positive brightness curve, maybe established in which the parameters are respectively densityrepresentative signal amplitude versus screen brightness. Since it isthe output of the photo-curve amplifier which is to be used to drive thecathode-ray tube, then the transfer characteristic of the photo-curveamplifier is made to have the characteristics shown to be required bythe density signal versus screen brightness curve, only, of course, thetransferl characteristic curve is input voltage versus the outputvoltage required to drive the cathode-ray tube grid (through thesubsequent linear amplifier) to obtain the required brightness. Sincethe transfer characteristic of the cathode-ray tube (i. e., signal atgrid-to-screen brightness) is not linear, the transfer characteristic ofthe photo-curve amplifier is further determined to take these departuresfrom linearity into consideration. The transfer characteristic of thephoto-curve amplifier is substantially as shown in Figure 2F. This curveof the relationship between the voltage input to the voltage outputrepresents both the desired relationship between screen brightness andnegative density as well as the correction or predistortion required tocompensate for the cathode-ray tube transfer characteristic.

` The photo-curve amplifier output is applied to a fixedgain linearamplifier 3S, 38, 38 whose input is linearly related to its output. Thefixed-gain linear amplifier output signal then again has its pedestalclamped to zero volts by another pedestal clamping circuit 40, 40', 40".This signal is applied to the grid of a cathode-ray tube 42, 42', 42".This cathode-ray tube is biased so that zero signal represents maximumillumination, and the more negative the signal, the less theillumination of the screen. The curve showing the transfercharacteristic of the "cathode-ray tube is represented by Figure 2G. Itis a curve lof logarithm of the screen brightness against the inputvoltage. The cathode-ray tube at the output of each channel has a screenwhose color is determined by the primary color with which the colorseparation negative for the channel is associated. Accordingly, thethree cathode-ray tubes may provide red, green,.and blue light. Thethree cathode-ray tubes have a common deflection voltage source 44synchronized with the deflection circuits '11 of the flying-spotscanner. The reason for this, of course, is that it is `desired that thecathode-ray beams for three tubes be substantially simultaneouslypositioned and deflected at all times with the flying-spot scanner beam.The three tubes are positioned as shown. Two mirrors 46, 48 are usedwhich are at 45 angles with respect to the tube opposite which they areplaced. The two mirrors are also positioned so that the light from thetwo tubes may reach the eye "50 of an observer at the same time and inthe same position as the light from the third tube which is beingdirectly observed through the two mirrors.

In order to overcome the white retrace lines of a picture which isobtained as a result of the pedestal between yideo signals beingclampedat picture white, a blanking pulse from a blanking-pulse amplifier 52 isprovided during each pedestal interval to overcome the effect of thispedestal and maintain the tube screens dark during the retrace interval.This blanking pulse may be applied .as shown to the cathode of eachone.of the television tubes. The amplifier 52 is also'synchronized properlywith the `deflection circuitry. It will be appreciated that, in view ofthe fact that the phosphors of the vthree tubes are selected to providethe primary colors, these can be operated to provide White orsubstantially any other required colors by properly mixing the outputfrom the three tubes. Furthermore, if desired, instead of using threetubes having three 4different phosphors, it is possible to use threetubes having a white phosphor and three different lters, a singletric-olor tube, or a single White screen tube with rotating filters infront thereof and the signals supplied from the three channels to thetube grid on a time-sharing basis and in synchronisrn with the rotatingfilters. It would further be possible to obtain the tricolor displayfrom the three images of three projection systems arranged tosuperimpose in register on a common viewing screen. These are several ofthe eXpedients used to present a color television picture and areapplicable herein.

Reference is now made to Figure 3 which shows -a series of curvesindicative of the transfer characteristics from the input up to variouspoints in a typical channel of the system. For example, Figure 3 isrepresentative of the video signal output of the video preamplifierprovided when a negative, of the type represented in the curve of Figure2, Which ranges from a minimum to a maximum density is scanned. Figure3A shows the video signal output of the logarithmic amplifier 24 forthis type of signal. It will be appreciated that the signals presentedto the logarithmic amplifier are representative of the transmissioncharacteristics of discrete areas of -a negative. Since the l. Denslty Dlog transmission these signals are converted to density-representativesignals by the logarithmic amplifier; Accordingly, the output of thelogarithmic amplifier may be read by a linear metier in terms ofdensity, since it represents the density of the discrete area of thenegative being scanned at the particular instant of the reading.Accordingly, the system shown and included up to the output of thelogarithmic amplifier for each channel may be considered an electronicdensitometer. l'

For the three clipping levels shown in the transfer characteristic curveof Figure 2D, three different curves of negative density versus thevoltage output obt-ained from the clipper are shown in Figure 3Balthough the same negative is scanned in each instance.

As stated previously, the complete video signal, as in televisionpractice, consists of a pedestal, a negativegoing video signal, anotherpedestal, another negativegoing video signal, etc. The pedestals occurduring the blanking intervals during line retrace. The pedestal clipperclips these pedestals at a desired negative level. The subsequentpedestal clamp serves to move the entire signal so that the remainingunclipped pedestal portion` is clamped to zero voltage. Of course, thevideo signal is moved closer to Zero along with its -unclipped pedestalportion. Effectively, then, the pedestal clippermaybe varied to move thevideo signal any desired value closer to zero voltage level or to leaveit at its most negative position. Since, as previously described, thecathoderay tube at the output of a channel is biased to provide itsbrightest light output when there are zero volts applied to its grid andto decrease is light output with increasingly negative signals appliedto its grid, the pedestal clipper can be said to control or establishthe brightness range for the picture resulting-from the video signalsbeing applied to the cathode-ray tube grid via the pedestal clipper.Increasing or decreasing the brightness or illumination level of a lightsource used to print a positive from a negal tive has'this effect.Therefore, the control of the pedestal vclipper may be calibrated inunits corresponding to the level of illumination required of a printinglight to achieve the desired photographic exposure. lt will also beunderstood that a fixed level of illumination may be used for a positiveprint and the time of exposure may be varied. For such a situation, theprinter-light control may be calibrated in terms of time of exposure fora predetermined level of illumination.

Figure 3C is representative, for the three clipping levels shown inFigure 3B, of the output of the variablegain linear amplifier for theinput to a channel obtained from a negative whose density varies, aspreviously indicated. Figure 3D shows the three different curvesobtained when the clipping level is held constant and the gain of theamplifier is varied. Figure 3E shows the channel transfer characteristicat the output of the photocurve amplifier for three different clippinglevels.. Figure 3F shows the output of the photo-curve aniplifier-forone clipping level with three dilerent gain positions chosen for thevariable-gain amplifier. Figure 3G and Figure 3H, respectively, showcurves of the logarithmpf of the screen brightness with respect to thenegative density for three different levels of the pedestal clipper andfor three different positions of the gain control of the variabie-gainamplifier when the pedestal clipper level is maintained constant. Theselast curves then represent thc transfer characteristics of for threedifferent pedestal levels and for three different settings of thevariable amplifier. it can be appreciated from the curves of Figure 3Ghow, for each different setting of the pedestal clipper, the samepicture brightness range is provided although the negative densityproviding that range is greater or lesser-the same effect that may beobtained by increasing or decreasing the level of illumination of aprinting light. The log screen brightness versus negative density curvesof Figures 3G and 3H represent the characteristics of each channel. FromFigure 3H it should be appreciated that, as the gain of thevariable-gain linear amplifier is increased, the greater the brightnessrange with which a given negative density range is reproduced as apositive, and inversely a decrease in amplifier gain provides a decreasein brightness range for the reproduction as a positive of the samenegative density range. This is indicated by the different curve slopesin Figure 3H. In effect, therefore, the variable-gain amplifier providesa means for controlling or determining the contrast of the positivepicture shown on the face of the cathode-ray tube. Accordingly, theamplifier-gain control may be called a contrast control and may becalibrated in terms of contrast.

A further appreciation of the operation of this invention may beobtained by seeing what happens at various points in a channel to avideo waveform obtained by scanning a line of a negative having the testpattern densities shown in Figure 4. The signals are shown against ascale of relative video voltage values with white or maximum screenbrightness being obtained with zero volts applied to the grid and blackor minimuiri screen brightness being obtained with a relative videovoltage value of l.00. Figure 4A shows the video waveform obtained atthe output of the video preamplifier. Figure 4B is illustrative of thevideo waveform obtained at the output of the logarithmic amplifier. Thiscurve then has its pedestal clipped at a level determined by theprinter-light control. The resulting signal is shown in Figure 4C. Theoutput of the variable-gain amplifier is shown in Figure 4D for threedifferent gain-control settings corresponding to the three settingsshown in curves of Figure 3D. The output of the photo-curve amplifierfor only one of the settings is shown in Figure 4E. Figure 4F shows thepositive picture which is seen on the cathode-ray tube screen at theoutput of the channel.

It will be appreciated that the system described in using electronictechniques presents a positive picture from a photographic negative. Thepositive picture reproduces the colors of the original when signals,corret'ne channel spending to those obtained by scanning three colorimage aspect negatives with the fiying-spot scanner, are respectivelyapplied to the three channels. By adjusting the printer-light controland the contrast control in each channel, the color brightness andcontrast of the positive picture presented, and thereby the overallcolor balance, may be determined. In accordance with known photographictechniques, contrast may be determined from a knowledge of thecharacteristics of the material on which a positive print is to be madetogether with the development procedure used with it. Thus, differenttypes of positive stock may have different contrasts, or a given type ofpositive stock may be developed in different ways to yield differentcontrasts. These may be given different numbers and these numbers can beused for calibration of the contrast control. With the printer-lightcontrol and the contrast control calibrations established, the correctexposure and contrast may be obtained readily for any set of negativesby scanning them and adjusting the controls in each channel until apositive picture is presented having the desired color balance andcontrast. The control settings in each channel are then read andemployed in the actual printing of the positives.

A preferred manner of employing this system for providing printerexposure data for photographic printing of motion pictures is asfollows: Motion pictures of a particular setting and action are taken.Separation negatives of the motion pictures taken at the set are thendeveloped and scanned by the flying-spot scanner, and the resultingsignals are applied to the respective color channels. The picturepresented by the cathode-ray tube apparatus is viewed alongside of anoptically projected reference of previously processd film of' likecharacter. The printer-light controls and contrast controls may then bevaried until the picture seen on the cathode-ray tube apparatus has thedesired color balance and contrast substantially as shown in theoptically projected reference. The printer-light and contrast controlsettings for each channel may then be read or recorded and then used inprocessing, and the finished prints will have all the qualities of thereference print.

Although the embodiment of the invention has been thus far described asproviding printer exposure data for photographie printing when threeseparate black and white color separation negatives are scanned by theflying-spot scanner, this is not to be construed as a limitation on theuse of the apparatus. Actually, any means for deriving signals of thetype obtained when the color Separation negatives are scanned can beemployed, and these signals may be applied to the respective channels toproduce a color positive picture. The signals may also be obtained fromany of the multilayer negatives used in color photography such asintegral tripacl; stock of the color negative type by scanning thesignal negative with a flying-spot scanner and splitting the resultantbeam into three with a beam splitter and then using a different tilterin front of each phototube .so that only the signals representative ofthe color components which each channel is designed to control areapplied to that channel. lf preferred, diehroic mirrors may be used, inthe manner well known in the art, to split the light beam after it hasbeen passed through the negative being scanned into three beams each,representative of the color component which each of the channels is tocontrol. Accordingly, when reference is made herein to separatenegatives, the same intended to include multiple emulsion negatives on asingle base.

Without any modifications this invention may be used to provide exposuredata for the three separate black and white negatives obtained frommultilayer stripping film. It should be obvious that a single channelmay be used for providing data and also that two channels may be usedfor providing data from bipack film, the cathoderay tube screenphosphors being selected to provide the proper color, or whitecathode-ray tube screens being used with proper color filters beingpositioned-in front-thereof. It. should be appreciated, therefore, thatthe inven- .tion is useful to provide printer exposure `data fromsignals of the proper type regardless of the source of said signals orthe original recording medium from which the signals of the proper typeare generated. These signals, for example, may be recorded on magnetictape. These lsignals may also be obtained by scanning color papernegatives, using refiection techniques to derive the signals. The aboveare just a few of the uses of this invention in both still and motionpicture photography. The fact that only these are recited should not beconstrued as a limitation since many other uses, such as in lithography,will occur to those skilled in these arts and may Still be Within thespirit and scope of this invention.

As previously stated, circuits for the flying-spot scanner tube and therespective phototubes and video preamplifiers are well known in thetelevision field and may be found described under the name flying-spotcamera.

Figure is a circuit diagram of the logarithmic amplifier, pedestalclamp, and pedestal clipper whichare ernployed in the embodiment of theinvention. As previously stated, the logarithmic amplifier has atransfer function wherein its output is substantially proportional tothe logarithm of its input. To achieve this, curve-fitting techniquesare employed of the general type described in Waveforms by Chance etal., page 315, and published by ,the McGraw-Hill Book Company. The videooutput from the preamplifier 20 is applied to the logarithmic amplifierinput which consists of two stages of video amplification 60, 62including two amplifier tubes with feedback between the plate of thesecond and the cathode of the first,in order to assure linearity. Theoutput from the second of these two video amplification stages isapplied to a first curve-fitting section 63. The first section consistsof a cathode follower 64 having its cathode coupled to the grid of asucceeding cathode stage follower 66 via two resistors 68, 70 in series.A first 4diode 72 has its cathode connected to the junction of the tworesistors 68, 70 through a third resistor 74 and its anode connected tothe cathode of a cathode follower tube 76. A second 'diode 78 has itsdiode 78 has its cathode connected through a resistor 80 to theconnection with the grid of the succeeding cathode follower stage 66.This diode also has bias applied to its anode by means of a cathodefollower stage 84. The output of the first curve-fitting section 63 isapplied to a second curve-fitting section 86 which is similar to thefirst. The output of the second curve-fitting section 86 is applied totwo stages 88, 90 of video amplification which Ihave the same circuit asthe first two stages 60, 62. The output is applied to yanothercurve-fitting section 92 in similar to the first and again consisting ofa cathode follower 94 whose output is coupled to a succeeding stage 96via two series resistors 98, 100. Two diodes 102, 104 are coupledthrough other resistors to these two resistors and are biased by meansof cathode followers 106, 108. One more curve-fitting diode 110 isemployed at the output of the third section so that, in all, sevencurve-fitting diodes are employed. These diodes are biased to provide atransfer characteristic as shown in Figure 2C. This is obtained bybiasing the diodes increasingly negative so that, instead of a linearinput versus output curve, the input versus output curve is bent byreason of the diodes permitting amplification of increases in signals ina nonlinear incremental fashion. The output of the last curvefittingsection is applied to the pedestal clipping section -26, which will bedescribed in greater detail later. Cathode followers are used to biasthe respective curve-fitting diodes in order to provide the utmost instability of'said biasing and to preserve the D. C. component.

VThe circuit shown below the logarithmic amplifier consists of ltwoclamping or D. C. restoring circuits. ,These are represented by therectangle 22 in Figure 1. lfhe clamping action in this instance is notpassive, de-

pending on average signal value, but is active and is obtained using thehorizontal sync signal. Clamps of this `type may be found described inTelevision Engineering by Fink, pages 298-299, and published by theMcGraw- Hill Book Company. This clamp uses four diode rectiers 110, 112,114, 116 connected in bridge fashion. The horizontal sync signal whichis used to defiect the flyingspot scanner beam is amplified by twostages of amplication 120, 122. The output is applied to two separatephase-splitting stages 124, 126 whose output is respectively applied totwo opposite terminals 128, 130 of each rectier bridge. A bias isapplied to a third one 132 of the remaining diagonal terminals of eachbridge from a fixedly biased cathode follower stage 134. The output fromthe remaining diagonal 136 of one of the bridges is coupled to the gridof the first cathode follower 64 employed in the first curve-fittingsection. The output from the remaining diagonal 136 of the other bridgeis coupled to the grid of the cathode follower 94 following the secondvideo amplifier section of the logarithmic amplifier. This assures thatthe signals being applied to the curve-fitting portions of thelogarithmic amplifier are at all times clamped to the desired D. C.level since the clamping signal is renewed with each line.

Figure 6 is a circuit diagram of the printer-light control for onechannel. It consists of two voltage divider networks 140, 142 followedby a cathode follower tube 144. The first voltage divider is connectedacross a source of bias potential. It includes two fixed resistors 146,148 in series with a potentiometer 150. The potentiometer tap isconnected in series with the second voltage divider consisting of twofixed resistors 152, 154 and two potentiometers 156, 158 in series. Thepotentiometer 150 in the first voltage divider is used to adjust roughlythe current fiowing through the second voltage divider. Thepotentiometers 156, 158 in the second voltage divider have their valuesselected to provide, respectively, coarse and fine controls for settingup the bias provided to the grid of a cathode follower tube to which thefine control potentiometer arm is connected. All the potentiometers arein the printer-light control but, in practice, once the two coarsecontrols are set, they are rarely adjusted further. Thus the rotation ofthe arm of the potentiometer 158 connected to the grid of the tube maybe calibrated in well-known fashion by means of a dial (not shown)either in exposure time or in printer-light illumination level. Thecathode follower 144 is used to bias the three diodes 160, 162, 164 inFigure 6, representative of the three diodes coupled between the lastcurve-fitting diode in the logarithmic amplifier and an output cathodefollower tube 166. These three diodes may be considered as the pedestalclipper. The cathode of the cathode follower tube 144 in theprinter-light control is coupled to the cathodes of three diodes 160,162, 164 shown in the logarithmic amplifier of Figure 5. Thus it setsthe level which a signal is required to exceed in order to be applied tothe grid of the output stage 166. It should be noted that the biasdiodes used in connection with the printer-light control and pedestalclipper are reversed from those used in the curve-fitting sections. Theclipper control diodes are biased and connected so that if the signalsapplied are more positive than the bias, the diodes will conduct andthus clip off the more positive peaks of the pedestal of the videosignal. This action is illustrated in Figures 4B and 4C.

The photo-curve amplifier circuit is substantially identical with thelogarithmic amplifier circuit shown in Figure 5. The bias applied to thevarious diodes employed in the curve-fitting sections in this instance,however, is such as to provide a transfer characteristic in accordancewith the curve shown in Figure 2F. Of course. no clipping section isneeded for the photo-curve amplifier.

Figure 7 is a circuit diagram of the variable-gain linear amplifier 30and also shows the contrast control 32. The amplifier consists of twostages of video amplification 170,

'inademen l1 172 and an output cathode follower stage 174. The gain ofthe amplifier is carefully controlled by controlling the feedbackbetween the anode of the second video stage and the cathode of the firstvideo stage. This controlled feedback is obtained by connecting theanode of the second video stage 172 through two series-connectedresistors 176, 173 to a potentiometer 180. The potentiometer resistancehas one end connected to the cathode of the first stage 170 and theother end connected to a resistance 182 which in turn is connected toground. The variable arm of the contrast control potentiometer 180 iscoupled to an indicator (not shown) in well-known fashion. This is thencalibrated in terms of contrast versus amount ot potentiometer armrotation.

A circuit diagram for a fixed-gain linear amplifier is not shown sincevideo amptihcrs having the required qualities of linearity are wellknown. The variable-gain linear amplifier, the circuit of which is shownin Figure 7, can be and has been used for this purpose. Once itscontrols are set at the proper gain level, they are not adjustedfurther. The pedestal clamp 34 associated with the linear amplifier maybe ot" the same type shown in the circuit diagram in Figure 5,

Power supplies, detiection circuits, and blanking circuits lor theflying-spot scanner and the three cathode-ray tubes represented byrectangles are not shown in detail since these are well known in thetelevision art and are commercially purchasable.

An system using negatives from which color positives are to be made catiemploy the embodiment of the invention shown here. It is required merelythat electrical signals be generated representative of either theoptical transmission or optical density of the negatives from which acolored positive picture is to be made. These optical transmissionsignals can then be employed in the manner taught hccin to produce apositive color picture. Optical density signals can be applied to thesystem after the logarithmic anipliher to achieve the desired results.

Another feature of this invention can be seen by referring to Figure S.Figure 8 shows a resistance network which. it rstutired, may heconnected between and in channels at the output of the variable-gainlinear amplilier. This network broadly serves the purpose of effectivelymodifying the positive picture obtained with this system so that it moreaccurately represents either the picture with which it is being comparedor the results to be obtained with the finished positive picture.

An analysis of color prints indicates that colors, especially saturatedcolors formed by dyes used in a suhtractive system. tend to he d gradedin purity and reduced iront their proper relative brightness because thedyes et one primary color have residual absorption within the wavelengthregion of the other primaries. Figure 9 shows typical spectralabsorption curves of three silbtractive dyes used in making positivepictures. The curves represent photographic density versus thewavelength in millimicrons and the regions of overlap of thel curves arequite apparent. lt can be seen therefore how much density or darkeningeach dye of a typical subtractive system produces within the wavelengthregion of the other dyes. To compensate for the darkening effect of thedyes within each others wavelength region, the circuit shown in Figure 8may be employed to simulate the cross-channel subtractions found in thedye systeni. The circuit permits [ceding controlled amounts et? signalwhere the voltage crossfeed is proportional to negative density from onechannel to each of the others. It will bc recalled that each channelderives its original 'nal modulation t'ioni a photographic negative;that is to say. where the negative has low density the correspondingsignal is large, and this must drive the cathoderay tube dark in orderto correctly produce a positive picture. Accordingly, increasing asignal by adding thereto goes in the direction of darkness, and thecross- 3.2 channel exchange of signals works in the desired direction tosimulate dye overlaps in the subtractive print.

It will be noted that each channel is connected to every other channelthrotfth two resistive circuits, each consisting of a resistor 26E- inseries with a potentiometer 20L-296. If it is assumed that the firstchannel will present the color red at its output, the second channel thecolor green, and the third channel the color blue, then the crossteedsfrom one channel to the other control the simulation of the absorptionelects as follows: potentiometer ZOi-blue absorption by magenta dye;potentiometer 20E-blue absorption by cyan dye; potentiorneter 203-grecnabsorption by cyan dye; potentiometer ,2M-red absorption by magenta dye;potentiometer 20S-green absorption by yellow dye; potentiometer 20o-redabsorption by yellow dye.

The curves in Figure 9 bear similar reference numerals to thepotentiometers which are used to correct for the overlap etlect whichthey rep rscnt.

The potentiometers in thc cross-channel connections are adjusted inaccordance with the information derived from the spectral-absorptioncurves to provide the proper amount of cross-channel signal for a givenLtmplitudc channel signal and confirmed by visual appraisal of colorualities. ln addition, adjustable attenuators 207, 208, Ztl are insertedin se s in each channel. 'ihc purpose of these is to adjust the over-allsignal voltage of each channel to the sanic level it would have if therewere no crossfeed. These are substantially the same as contrastcontrols. lf one of them should be set to zero (i. e., no attenuation)and the signal level of that channel uld increased by the contributionfrom another channel, the electronic color picture would be found toexhibit increased contrast since the brightness swing would be greaterbecause of the other contributed signals. It is necessary, therefore, toadjust these controls to compensate for the voltage built up bycrossfeed. Once all of the controls, both crossfeed and attenuation, areadjusted. these settings remain fixed so long as the equipment isrequired to reproduce pictures made by a given subtractive dye system.New settings' are required to niateh pictures or a different colorprocess. If a number of different color processes are employed, thesenetworks may be made up as separate items which are preset and eitherplugged or switched in, in accordance with the systems in use.

Figure 10 is a circuit diagram of a preferred resistance networkarrangement which achieves the same results as are achieved with thenetwork shown in Figure 8 but does not produce the variations incontrast which require the use of the attcnuaters 207, 26S, and 299. Thepotentiometers in Figure l0, which function to control the semerespective crossiceds, hear the same reference numerals as thepotcntiometers shown in Figure 8. The adjustment of these potentiometersis accomplished in the same manner as is described for the adjustment ofthe crossfeed potentiometers in Figure 8. However, in view of thecascade connections of the crossfced potentiometers in Figure l0, i. e.,each potentiometer 202, 26st, 205 is connected between a different twochannels and the respective third pcttnititnnetcrf; 20L 203, Zut() areeach connected between the remaining channel and the potenticmetric armof a potentiometer connected across two channels, from the seriesconnection shown in Figure 8, no contrast changes occur and the channelsignal levels need not be attentuated by a separate set of attenuators.Sets of plug-in units of this potentiometer arrangement may also be madeup for each different color process, if desired.

Accordingly, there has been shown and described a novel and usefulsyteni for reproducing electronically, in color, positive pictures frominformation derived from signals corresponding to the transtssion ofcolor separation negatives. By employing the novel principles andstructure described and shown herein, it will be apparent thatinformation for timing and processing the chemical development of colorpictures, both for still and motion picture photography, may beobtained.

What is claimed is:

1. An image translating system comprising means to generate electricalsignals representative of the light transmission of discrete areas of aphotographic negative, electronic means responsive to said electricalsignals to present the corresponding positive picture of said image,means to control the contrast of said positive picture, and means tocontrol the brightness of said positive picture.

2. An image translating system as recited in claim 1 wherein said meansto control the brightness of said positive picture includes an indicatorvariable therewith and calibrated in terms of exposure.

3. An image translating system comprising means to generate electricalsignals representative of the light transmission of discrete areas ofcolor image aspect negatives of said image, electronic means responsiveto said signals to present a corresponding positive picture in color ofy said image, means to control the positive contrast of each primarycolor in said picture, and means to control the color balance of saidpicture. t

4. An image translating system as recited in claim 3 wherein said meansto control the color balance of said picture includes an indicatorcontrolled by said means and calibrated in terms of exposure.

5. An image translating system comprising means to generate electricalsignals representative of the optical density of discrete areas ofdifferent color image aspect negatives, and electronic means to convertsaid signals to point-by-point variations of colored light sourcescorresponding to the colors represented by the diierent color imageaspect negatives to present a colored positive picture of said image,said last named means including means to control the contrast of eachcolor of said colored positive picture, and means to control thebrightness of each color in said colored positive picture.

6. A system for presenting a positive picture of an I object withcathode-ray tube apparatus from signals representative of the opticaldensity of discrete areas of a photographic negative of said objectcomprising means to modify said signals in accordance with a desiredrelationship between negative density and screen brightness of saidcathode-ray tube apparatus, and means to apply said.

modiied signals to said cathode-ray tube appartus to present a pictureof said object.

7. A system for presenting a positive colored picture of an object withcathode-ray tube apparatus from signals Arepresentative of the opticaldensity of -discrete areasof ,color image aspect negatives of saidobject comprising means to modify said signals in accordance with adesired relationship between negative density and screen brightness ofsaid cathode-ray tube apparatus, and means to apply said modied signalsto said cathode-ray tube apparatus to present a positive picture of saidobject in color.

8. A system for presenting a positive picture of an object withcathode-ray tube apparatus from signals representative of the opticaltransmission of discrete areas of a photographic negative comprisingmeans to modify said signals to be representative of the density of saidnegative, means to modify said density representative signals inaccordance with a desired relationship between negavtive density andscreen brightness of said cathode-ray j tube apparatus, and means ltoapply the output of said last named means to said cathode-ray tubeapparatus to ship 4between'negative density and screen brightness .of

-said cathode-'ray tube apparatus, and means to apply-the output of saidlast named means to said cathode-ray tube apparatus to present saidpositive picture in color.

l0. A system for presenting a positive picture of a colored object withcathode-ray tube apparatus from signals representative of the opticaltransmission of discrete areas of color image aspect negatives madelfrom the colored object comprising an image translating channel foreach dilerent color image aspect each of which includes means to modifysaid signals to signals representative of the density of said negative,means to modify said density representative signals in accordance with adesired relationship between negative density and screen brightness ofsaid cathode-ray tube apparatus, said cathode-ray tube apparatusincluding a cathode-ray tube for each channel, each tube having a screenproviding illumination having the color associated with the negativeproviding signals for the channel, means in each channel to apply saidmodified density representative signals to the cathoderay tube in thechannel, and means to super- ,impose'th'e light outputs from all thecathode-ray tubes to provide a positive colored picture Aof said object.

ll. A system for presenting a positive picture of an object withcathode-ray tube apparatus from signals representative of the lighttransmission of discrete areas of a negative of said object comprisingmeans to apply a logarithmic correction to said signals to obtainsignals representative of the optical density of said negative, means tocontrol the average value of said density representative signals todetermine the brightness of the positive picture, means to amplify theoutput of said average value controlling means, means tocontrol the gainof said means to amplify, to determine the contrast of said positivepicture, meansto modify the output of said means to amplify inaccordance with a desired negative density 4to cathoderay tube screenbrightness characteristic and to compensate for the transfercharacteristic of said cathode-ray tube apparatus, and means to-applythe output of said means to modify to said cathode-ray tube apparatus topresent a positive picture of said object.

l2. A system as recited in claim l1 wherein said means to control theaverage value of said density representative signals includes anindicator coupled to said means to be variable therewith, said indicatorbeing calibrated in terms of printing exposure required for saidnegative,

13. A system for presenting a positive colored picture -of an objectwith cathode-ray tube apparatus from sigvnals representative of thelight transmission of discrete .areas ofcolor image aspect negatives ofsaid object comprising a separate channel for the signals from each vnegative, each channel having a logarithmic network to which saidsignals are applied, means to clip at a desired level the pedestal ofthe output signals from said logarithmic network to control the colorbrightness of the output from a channel, an amplier to which the outputof said means to clip is applied, means to control the gain vof saidamplier to control the contrast of the output from said channel, andmeans to modify the output of said m-eans to amplify in accordance witha desired negative density to cathode-ray tube screen 'brightnesscharacteristic and to compensate for the transfer characteristics ofsaid cathode-ray tube apparatus; and means to apply said modifiedsignals from each channel to said cathoderay tube apparatus to present apositive colored'picture.

14. A system as recited in claim 13 wherein said means to clip at adesired level includes an indicator coupled to vary with the desiredclipping level, said indicator being calibrated in accordance withprinter-light illumination units required to provide a positive printhaving substantially the same color brightness.

l5. In a system for electronically presenting a positive colored pictureof an object from signals representative of the light transmission ofdiscrete areas 0f three dassesses color image aspect negatives where thesignals for each color are translated in a separate channel to controlcathode-ray tube apparatus to provide an additive picture presentation,means to modify said additive picture presentation to resemble a desiredsubtractive color picture presentation comprising network means coupledbetween channels to feed signals therebetween to simulate the overlapeffects on one another of primary color dyes used in said desiredsubtractive color picture, said network means including a rstpotentiometer means coupled between a first and second of said signals,a second potentiometer means coupled between said first and a third ofsaid separate channels, and a third potentiometer means coupled betweensaid second and third of said channels.

16. A system for presenting a positive colored picture of an object withCathode-ray tube apparatus from signals representative of the opticaldensity of discrete areas of color image aspect negatives of said objectcomprising a separate channel for the signals for each different colorimage aspect negative, network means coupled between channels to feedsignals therebetween having an amplitude to achieve effects on thesignals in the channels representative of the overlap effects of primarycolor dyes used in a desired subtractive system on one another, means ineach channel to modify the signals in said channel in accordance wtih adesired relationship between negative density and screen brightness ofsaid cathode-ray tube apparatus, means to modify the signals in eachchannel to compensate for the transfer characteristics o1 saidcathode-ray tube apparatus, and means to apply said doubly modifiedsignals of all the channels to said cathode-ray tube apparatus topresent a positive picture of said object in color.

17. A system as recited in claim 16 wherein each channel includes meansto attenuate the signal levels in each channel to compensate for thesignals fed between said channels.

18. A system for presenting electronically a positive colored picture ofan object with cathode-ray tube apparatus from signals representative ofthe light transmission of discrete areas of color image aspect negativescomprising a separate channel for the signals from each color imageaspect negative, each of said channels including a logarithmic circuitto which said signals are applied, a peak clipping circuit coupled tothe output of said logarithmic amplifier, means to control the clippinglevel of said peak clipping circuit to determine the color balance ofthe picture finally presented, an amplifier, means to control the gainof said amplifier to control the contrast of the picture finallypresented, network means coupled between said three channels at theoutput of said amplifier in each channel to feed signals therebetweenrepresentative of the overlap effects of primary color dyes to be usedfor a subtractive representation of said colored picture, attenuatormeans in each channel to compensate the signal levels for the effects ofsaid network means, means in each channel to modify the output of saidattenuator in accordance with a desired negative density to cathode-raytube screen brightness characteristic; and means to apply the output ofeach said means to modify circuit means to said cathode-ray tubeapparatus to present a positive colored picture.

19. A system for presenting electronically on cathoderay tube apparatusa positive colored picture of an object from color image aspectnegatives made from said object comprising a separate channel for eachcolor image aspect negative each including means to generate signalsrepresentative of the light transmission of corresponding discrete areasof each negative, a logarithmic amplifier, means to apply said signalsto said logarithmic amplifier to obtain signals representative of thedensity oi" said discrete areas, a pedestal clipper, means to apply saiddensity representative signals to said pedestal clipper, means tocontrol the clipping level of said pedestal clipper to determine thecolor balance of the picture finally presented, calibrated meanscontrolled by said means to control the clipping level and calibrated interms of i1- luinination intensity required for obtaining a positiveprint of similar color brightness from the negative associated with saidchannel, a variable-gain linear amplifier coupled to receive output fromsaid pedestal clipper', means to control the gain of said linearamplifier to determine the contrast of the picture finally presented,photo-curve amplifier means to provide an input to output characteristicrepresentative of a desired relationship between negative density tocathode-ray tube screen brightness and the compensation required for acathode-ray tube transfer characteristic, means to couple the output ofsaid linear amplifier to said photo-curve amplifier means, and acathode-ray tube coupled to receive output from said photo-curveamplifier means, said cathode-ray tube having a screen providing a colorcorresponding to the primary color represented by the color image aspectnegative associated with said channel, and means to combine the imagesdisplayed on each cathode-ray tube screen into a single colored pictureof said object.

20. A system as recited in claim 19 wherein said means to apply theoutput of said variable-gain linear amplifier to said photo-curveamplifier means includes a resistance network coupled between each ofsaid channels to feed signals therebetween representative ot the overlapeffects of primary color dyes to be used for a subtractivcrepresentation of said colored picture.

21. A system as recited in claim 20 wherein said resistance networkincludes a different first potentiometer connected across a differenttwo of said channels and a different second potentiometer connectcdbetween one of said channels and the potentiometric arm oi" a differentone of said first potentiometers which is not connected to said onechannel.

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